In the wireless communications market, due to the increasing demands not only for voice call services but also for mass data services such as various multimedia Internet services, Orthogonal Frequency Division Multiplexing (OFDM), Single Carrier Frequency Division Multiplexing (SC-FDMA), and Wideband Code Division Multiple Access (WCDMA) are attracting attention as wireless transmission technologies capable of meeting the above demands. These technologies are applied to standards such as IEEE 802.16e Wireless Broadband (WiBro) or Mobile Worldwide Interoperability for Microwave Access (Mobile WiMAX), Wireless Local Area Network (WLAN), and 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE).
OFDM is a kind of Multi-Carrier Modulation (MCM) that transmits signal information on frequency-domain subcarriers. Therefore, an actually transmitted signal is a time-domain signal that underwent Inverse Fast Fourier Transform (IFFT) on a symbol-by-symbol basis, and a signal after undergoing IFFT has characteristics that amplitude thereof is not maintained constant. Thus, in OFDM, a PAPR is very significant compared with that in other modulation schemes, and such characteristics are obstacles to efficient use of a PA.
A high-PAPR input signal may deviate from a linear operation range of a PA, causing distortion at an output stage of the PA. In this situation, to obtain the maximum output, a back-off scheme may be used that lowers power of an input signal so that the PA may operate in a linear operation range. However, in the back-off scheme, an increase in back-off value for lowering power of an input signal leads to an increase in power consumption, deteriorating efficiency of the PA. In this way, a high-PAPR signal reduces power efficiency or uses a high-spec PA, increasing hardware prices.
Therefore, a mobile communication system using MCM such as OFDM and SC-FDMA, or Single-Carrier Modulation (SCM), needs technology for efficiently reducing a PAPR which occurs when a plurality of signals are mixed. Methods for reducing a PAPR may include clipping, block coding, phase adjustment, and the like. Clipping, a conventional technique for reducing a PAPR, is a technique that maintains a phase of a time-domain signal having undergone IFFT, and restricts only amplitude thereof below a desired threshold level. However, in the clipping technique, an input signal is cut at a threshold level, causing non-linear distortion, and to compensate for the non-linear distortion, an additional process such as filtering may be needed. However, filtering leads to peak regrowth that re-grows the signal components cut by clipping, causing a PAPR to re-increase.
Therefore, more efficient technology for reducing a PAPR of an input signal is needed for a PA in a communication system using MCM such as OFDM and SC-FDMA, or SCM.